Ball bearings enhance rodless cylinder's performance

Hamel, MN--When a design engineer requires a compact, rugged means of moving a load, rodless pneumatic cylinders often solve the problem. But until recently, off-center loads that imposed bending moments on the load carrier represented quite a challenge for rodless cylinders.

To increase the load capacity of their firm's new BC3 Series™ rodless band cylinders, engineers at Tol-O-Matic Inc. place a recirculating ball bearing system in the cylinder's carrier. Riding on hardened steel guides, the ball bearings increase the load and maximum bending moment that a cylinder can handle.

BENDING MOMENT CAPACITY

MODEL

BORE SIZE (INCHES)

MAX. BENDING MOMENT (INCH-LBS)

MAX. Load (LBS)

M

Ms

Mv

Fy

Fx

BC215

1.50

500

275

200

180

N/A

BC3

1.50

1009

853

583

1091

630

Gary W. Rosengren, Tol-O-Matic's engineering manager, explains that to provide an outer race for the carriage ball bearings, "we take a hardened and ground bearing steel rail and embed it in the cylinder tube." The rail, which has a Gothic Arch structure (three radii), runs the length of the cylinder. It's located in a slot in the extruded aluminum tube. When assembly personnel bolt the cylinder together, the slot closes down upon the rail and captures it.

Another rail, mounted in the carriage and approximately as long as the carriage, provides the recirculating bearing's inner race. Balls traverse a path that carries them between the inner and outer rails, through U-shaped end pieces made from 6/6 nylon, and through a steel auto-recirculating tube in the carriage. The Class-20 steel balls never contact the carriage or cylinder tube, so they can't carve up the relatively soft aluminum. Tol-O-Matic personnel build the recirculating bearing at the factory. The system is lubricated for life. Below the BC3's carriage, engineers use the same design employed in the company's other rodless band cylinders.

Employing the bearing system dramatically enhances this rodless cylinder's balanced load capacity and its bending moment capacity. Further, says Rosengren, unit life under load is impressive: "We're looking at 20 million feet of linear travel," he says.

Other Applications

Vacuumized sheet transfer

Rotating pick-and-place elevator

Model BC3 cylinders can be up to 14 ft. That limit is set by the maximum length of the extrusions used by Tol-O-Matic. The steel rail that forms the cylinder side of the bearing race consists of butt-jointed sections of rail. Tol-O-Matic grinds their ends square, de-burrs them, and butts them.

Initially, Tol-O-Matic made the BC3 in only one bore size, 1.50 inches. The company will introduce 1-inch and 2-inch-bore units to complete the BC3 Series.

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